In most low voltage circuit breakers, a contact pair of a stationary and a movable electrical contact are touching one another in a closed state of the circuit breaker. If the electric path through the circuit breaker shall be interrupted, the movable electric contact is moved along a path of movement relative to the stationary contact such that an electric arc is formed in between the stationary and a movable electrical contact. The foot points of the electric are spot-like and rather stationary in an initial phase of the interruption process. For extinguishing the electric arc, several methods can be employed. Most of them have in common that the electric arc is driven along a set of conductor rails electrically connected with the stationary and a movable electrical contact towards a set of splitter plates where the electric arc is interrupted eventually.
A first approach resides in that the electric arc is driven towards the splitter plates by way of a stream of pressurized air.
A second approach resides in exposing the electric arc to a magnetic field, e.g. from a permanent magnet. Said magnet is employed for urging the electric arc away from the stationary and a movable electrical contact towards the set of splitter plates.
A third approach resides in designing the nominal conductor path as well as the at the stationary and the movable electrical contact such that the natural magnetic field of the current flowing through the conductor path exerts its power on the electric arc such that the electric arc is urged away from the stationary and a movable electrical contact towards the set of splitter plates. A close-up of the interruption portion of a representative of the third approach is shown in FIG. 1. That electrical contact system illustrated in FIG. 1 comprises a first electric contact 1 shown as an upper contact as well as a second electric contact 3 shown as a lower contact in an open state of the electrical contact system. The first electric contact 1 has a first contact carrier 2 that is electrically conductively connected with a first contact piece 3 having a first contact surface 4. Likewise, the second electric contact 5 has a second contact carrier 6 that is electrically conductively connected with a second contact piece 7 having a second contact surface 8. The first electric contact 1 and the second electric contact 5 are movable relative to one another along a switching path extending in a switching plane X-Z. The switching path can be linear or arcuate.
The first contact surface 4 and the second contact surface 8 touch each other in a closed state of the electrical contact system. The first contact surface 4 is displaced by an insulating distance 9 to the second contact surface 8 in an open state of the electrical contact system such that the desired interruption and safe electric insulation between the first and second contact is achieved. The first contact surface 4 and the second contact surface 8 extend transversely, i.e. perpendicularly to said switching plane X-Z in the direction of virtual plane X-Z. Once this electrical contact system is opened, an electric arc 11 evolves between the first contact surface 4 and the second contact surface 8. Since the current path of the nominal as well as of the interruption current path lead through the first electric contact 1 and the second electric contact 5 in a loop when seen in plane X-Z, the natural magnetic field of the interruption current 12 pushes the electric arc 11 from the left to the right. In other words, the natural magnetic field of the interruption current 12 exerts a pressure or force 13 on the electric arc 11.
The third approach may suffer the problem that the natural magnetic field of the current flowing through the conductor path exerts only little power on the electric path such that it may remain in between the stationary and the movable electrical contact for too long before moving towards the set of splitter plates, provided that the electric arc moves towards the latter at all.